1. Field of the Invention
The present invention relates to a solid-state imaging device and an electronic camera equipped with the solid-state imaging device.
2. Description of Related Art
Video cameras and electronic cameras are among the most popular consumer electronic products used by ordinary consumers today. These cameras are equipped with solid-state imaging devices such as CCD sensors and CMOS sensors. Such a solid-state imaging device includes a plurality of pixels, which generate signal charges in correspondence to the quantity of incoming light, disposed in a matrix pattern. The signal charges having been generated at the individual pixels or electrical signals corresponding to the signal charges are output to an external recipient device via vertical signal lines or the like, each installed in correspondence to a pixel column, in conformance to a drive signal output from a scanning circuit in response to an instruction issued by a timing signal generator.
Such a solid-state imaging device in the known art may also be capable of functioning as a focus detection device engaged in focus detection executed by adopting a split-pupil phase difference method (see Japanese Laid Open Patent Publication No. 2003-244712). This type of solid-state imaging device includes focus detection pixels disposed in addition to imaging pixels that output imaging signals to be used to form image signals expressing the subject image. The focus detection is executed through the split-pupil phase difference method by detecting the extent of image shift manifested by a pair of images formed with light fluxes having passed through the photographic lens at different positions based upon signals output from the focus detection pixels.
There is also a camera known in the related art that provides a live view display by displaying at a liquid crystal monitor a real-time motion picture of the subject image captured via a solid-state imaging device (see Japanese Laid Open Patent Publication No. 2007-184912).
When a solid-state imaging device such as that described above is engaged in focus detection while a live view is displayed, it may not always be possible to execute exposure over the length of time required to enable optimal focus detection. Namely, the image signals from the individual pixels must be output at a predetermined frame rate in order to display a motion picture in the live view display. However, if the photographing operation is being executed in a dark environment, for instance, light may not be received at the focus detection pixels in sufficient quantity to assure accurate detection of the extent of image shift manifested by the pair of images over the exposure period corresponding to the frame rate, resulting in failure in executing accurate focus detection.